In accordance with the USB OTG specifications, a device may use the USB interface and behave either as a USB host, communicating with other peripheral USB devices, or as a peripheral USB device providing a service or services to a USB host. One example of such a Dual Role Device (DRD), that is, a device that may operate as either a USB host or peripheral USB device, is a cellular telephone.
The USB OTG specification was designed to enable point-to-point connections between two devices and to reduce the USB 2.0 specification host support. Particularly, an OTG DRD is only required to support a single device. Further, the USB OTG specification describes a means for two devices to exchange host functionality, which is required for implementation of certain device use cases.
A problem exists, due to host functionality exchange, for devices that have debugging or data logging capability using the USB interface, for the purpose of aiding software development. For example, a device under development is typically attached to a personal computer (PC) running debugging or data logging software. Because the PC in such a configuration behaves as a USB host, the device under development must be connected and behave as a peripheral USB device. Therefore, the device under development must have a physical USB device connector. The problem is that, because the device under development has only a single physical connection, and must be connected to a PC host during debugging, the device cannot be simultaneously connected to a USB OTG device and therefore cannot be observed and debugged while interacting with a USB OTG device.
Some USB DRDs may have an alternative attachment means, such as an embedded debug port with a physical connector other than a USB physical connector, for connecting to debugging equipage. However, such connections are not always available on a device. It is undesirable to design a DRD to have a specialized debug port, in addition to a USB port, due to cost and product profile considerations. Further, even if a distinct debugging port is available, performance reasons may render the use of the port for USB debugging unviable. For example, if problems occur in a device under development when the device is connected to a second USB device and thus using USB OTG features, it is desirable to use software debugging features of the device under development to observe the USB interface.
Further problematic is that, even if a device under development comprises a separate means to connect to a PC for debugging, the function drivers within the test device are generally designed and written to handle a peripheral type connection. Thus, substantial modifications may be required to the device development support software, such that operation of the test device as a USB OTG host would be supported.
Therefore, a need exists for an apparatus in which a USB Host may be connected between two USB OTG devices such that the USB OTG connection is not interfered with, and further such that the communications between the two USB OTG devices may be monitored.